Gain control system



Jan. 12, 1943.

J. THORPE ,GALN CONTROL SYSTEM Filed March 12, 1941',

Hybrid INVENTOR I Elan Ilka/79 6 BY 2 a e ATTORNEY Patented Jan. 12, I h

' such systems. More particularlmthis invention Reterring to Fig. 1 of the drawing. the referthe circuit transmitting signals under varying 611T!" m' mm d UNITED STATES PATENT, OFFICE-1" Application M i-cu 12, 1941, Serial No. 382,961

. 5Claims.- (curs-44) Y v This invention relates toaisnalin systemsand a push pu'll arrangement'orpentode vacuum particularly to apparatus to adjust the 811111.01 tubes or thevariable mu type.

relates to arrangements for adjusting the gain ence character-i designates an input circuit of a repeater in a signaling system to compensate which supplieis modulated carrier currents which for variations in the transmission equivalent of are to be transmitted to in Output i conditions of temperature, th m a transformer Ti. the secondary oi which is con- In carrier signaling systems 'e un are nected to the grid and filament oi an often located at various points along the circuit tube The usual a bmlns better! lltransmitting slmls for increasing the level of hated i and a n er-Ci is o nected seri s the trans itted energy ova- 39mg the man a with '26 battery Bi in the grid chcuit Of the tube circuit, the amplitude oi the pilot current changmeted to the output circuit e battery ing in accordance with the changes in t t B: is the filament battery for the tube and the mission equivalent 0! the circuit. This pilot cur. bitter! e in 1%; plate battery. t rent is caused to actuate apparatus connected or A1058 W fi millmlted M t t; coupled to the amplifier to change the gain oi traversing the vcircuit there is a P110 mcurrent the amplinerinaccordance with thevarying am ich may be 0i. a freq y lying ou dong plitude or the pilot current. That is, as the pilot the s of m m 8ml: t current decreases in amplitude due to increased tween the i i s 1 nd a This nfl rren attenuation in the circuit, the gain adjusting g i8 mpllfled by the ho? al ng with the 81181- 1'' 18 then rectified form of gain regulating arrangement is provided currents- The 9110!? mm!!! by which the gain oi the associated amplifier-ls rectifier and the i periodically increased and decreased as long as m traverse h winding! M are Y Themr will be inserted into thebiasing circuit and re- 0 g g gg fi gw if f f f d moved. therefrom at more or less regular inbattery B the W current m 18 a I This-invention will be better understood from fifizg gbg bg :3: the detailed description hereinafter following, may w to permit vblme of the new when read in connection with the accompanying finite amount, Fig. 3 shows the invention applied maintain the gain of the tube large enough to to a pair of vacuum tubes of the three-electrode F overcome any ordinary changes in the t type and Fig. 4 shows the invention applied to sion equivalent oi the circuit supplying signals voltage of battery to the input circuit 01. As the level of the signals approaches its upper predetermined limit, the pilot current picked off through the transformer T: will be transmitted through transformer T4, rectified by rectifier R and impressed upon the winding of relay W. The rectified current may be suificient, however, to operate the relay W. When this happens the closure or the contact K: will cause the battery B4 to charge the condenser C1 through the resistor Z to the B4 and hence increase the negative'bias or the grid 01' the tube V. The negative bias on the grid of the tube V will then tend to rise to a value which equals the sum of the voltages of the'batteries B1 and 34. 'Due to the increasing bias on the grid, the gain oi the amplifier will be reduced progressively and as the pilot curent is thus reduced in amplitude, the

rectified current traversing the winding of relay .W will eventually become insufiicient to maintain that relay operated. Hence the contact K1 will be closed by the armature oi the relay. -When this happens, the charge on the condenser 01 will commence to be dissipated through the resistor Z, and would eventually leave the battery '31 as the only source of negative bias for the grid of the tube V. But as the amplifier gain gradually increases and approaches itsupper prescribed limit, the increased current rectified by the rectifier R will again cause the relay W to operate, again causing the condenser C1 to commence to become charged by battery B4. This will go on and on as described. Thus the voltage applied to the grid of the tube V will be limited by that of battery B1 on the one extreme and that of batteries B1+B1 on the.other, but in practice will be equal to 31 plus a certain portion of the voltage of B: represented by the charge which condenser C1, is permitted to accumulate through resistance Z by the cyclical operation of relay W actuated by the rectified pilot tone derived from the output of tube V through rectifier R. The operation and release of relay W will continue as long as the level of the transmitted energy reaches or approaches its predetermined limits.

If perchance the pilot current should be greatly reduced in amplitude, as would be the case, for example, when the level of the transmitted energy falls below the lower prescribed limit, then the rectified pilot current will be insufficient to operate the relay W. In that case the contact K1 will remain closed during that interval and the gain of the tube V will remain stationary at it maximum value. the transmitted energy should at any time rise above the upper prescribed limit, then the rectifled pilot current will maintain the relay W operated continuously. In this case the contact K2 will remain closed during the interval and the voltage of batteries B1 and B4 will together cause the amplifier to introduce its min mum gain. But barring these extraordinary changes in the level of the transmitted energy, the relay W will be supplied with current which varies between the values required to operate the relay and then to release it so that the battery 164 will supply negative voltage through the condenser C1 to the grid of the tube V at more or less irrregular in tervals.

In one arrangement set up according to this invention the amplifier was incorporated as part of a. Type C carrier signaling system. The tube V was of the 10l-D type, the condenser C1 of a capacity of 2 microfarads. the resistor Z of a 2 Moreover, if the level of megohm value, the battery B4 oi 22 volts and the relay W of the KS-6864 type. In practicing the invention the rectifier R may be of any wellknown type, i. e., either of the vacuum tube type, or of the copper oxide type, with or without an accompanying amplifier. It was also found that as carrier telegraph signals were transmitted through the tube V, such signals were satisfactorily reproduced, and, moreover, short hits did not interfere with the operation of the circuit to any appreciable extent. 1

Fig. 2 shows how a portion of the circuit of Fig. 1 may be modified to improve the operation of the arrangement described in connection with Fig. 1. It will be observed that two additional resistors Z1 and Z2 have been inserted into thedischarge circuit for the condenser C1. These resistors are relatively small, i. e., of about 1,000 ohms each. Additional resistors Z: and Z4 may also be interposed in the circuit of the leads of battery B1 as shown, and these resistors may also be of about the same order of magnitude.

The addition 01' such resistors will tend to prevent oscillations which might otherwise result in clicks in the circuits connected or coupled to the output circuit 02. Such resistors will also tend to prevent excessive erosion at the contacts K1 and K: of relay W. The additional resistors Z1 to Z4 are, of course, optional, and are not necessarily required in the operation of the system. They may be especially useful in cases where the voltage of battery B4 is relatively large.

The transformer T3 is shown bridged across the output circuit 02 in an arrangement employing but one stage of amplification. It will be under stood that other stages of amplification may be added ii desired, and that the pilot current may be obtained at any point along the circuit and fed back in such a way as to change the grid bias of the first tube of the system according to this invention.

Fig. 3 shows a modified circuit arrangement which may be used for the control of greater volumes of the signals. To accomplish this a push-pull or duplex type of circuit is employed.

The tubes of the push-pull or duplex circuit of Fig. 3 are designated V1 and V2. The plate circuit of these tubes are connected to the input terminals of a hybrid network HN. One pair of output terminals of the network HN forming the main output circuit 02 may extend to another repeater point. The other output circuit of the network HN is connected through a transformer Ts, a series tuned circuit of inductance L and capacity C2 and a transformer T1 to a full wave rectifier R1 which rectifies the pilot or carrier current selected by the series tuned circuit. The rectified current then flows through the winding L of relay W, the latter relay being operated or released depending on the magnitude of the rectified current. The condenser C1 is charged upon operation of relay W and discharged upon release of relay W as already described in connection with Figs. 1 and 2. The condenser C1 and battery B1 are common to the grid circuits of both cults Just described .on the signals and pilot current flowing through circuit is reduced to a nullity by the hybrid network EN.

Pig. 4 shows the invention applied to a pair oi nected through corresponding large resistors Zr andzeandaresistorzntothepositiveterminaloi a battery Be, the negative terminal oi which is connected to the cathodes of both tubes. The

condenser C: is bridged across resistor Z1. This condenser is charged by battery 13-; or discharged through resistors Z1, Z1 and Z: according to the operation or release oi relay W. i

The operation oi relay W controls the charge by battery B1 of condenser C: in manner described hereinabove; This condenser establishes a certain average potential across resistor Z1 which potential is eflectively in series with battery Be.

The battery Be and condenser Ca jointly establish the operating potential oi the screen grids with respect to the cathodes of tubes V: and V4 and hence control the gain oi these tubes at the desired values.

It will be understood that in Fig. 3 pentode types oi tubes such as V: and V4 oi Fig. 4 may be substituted ior tubes Vi and V: in which case their screen potentials may be fixed in the usual manner and their gains controlled by the ad- Justment oi the potential of the control grids.

While this invention has been shown and described in certain particular arrangements merely tor the purpose oi illustration, it will be under-v stood that the general principles oi this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1: In a carrier signaling system, the combination of an amplifier, means to continuously control the gain of said amplifier, said means including a rectifier and a relay having its winding connected to said amplifier through said rectifier so that rectified currents will fiow through said winding, said relay being responsive to the level oi the signals, said relay being operated as the signals reach an upper predetermined limit and released as the signals reach a lower predetermined limit, a condenser which is fully discharged, means for charging said condenser in response to the operation oi said relay to change the gain of said amplifier in one direction, and means for fully discharging said condenser in response tothe release of said relay to change the 7 gain of said. amplifier in the opposite direction.

2. In a gain controlsystem, the combination of a vacuum tube having a source of voltage to corn trol the gain of the tube, a condenser connected in series with said source 01 voltage, means for charging Said condenser so as to increase the eifective voltage in the circuit of said source oi voitage, means for fully discharging said condei'iser, means comprising a relay responsive to a rise in the level of the energy transmitted through said vacuum tube to a first predetermined value to on crate the charging means, means including said relay and responsive to a recession oi the level of the energy transmitted through said vacuum tube below a second predetermined value to operate thedischarging means, and a rectifier connecting said vacuum tube to the winding of said relay so passed current, a relay supplied by the rectified current, said relay being operated when the rectified current corresponding to a change in level in one direction exceeds a first predetermined value and released when said rectified current corresponding to a change in gain in the opposite direction recedes below a second predetermined value, a condenser connected in series with the grid biasing source of voltage, means responsive to the operation of said relay to charge said condenser so as to increase the bias of the grid electrode with respect to the filament electrode, ,and means responsive to the release of said relay to fully discharge said condenser.

4. Gain control apparatus for a system transmitting modulated-carrier currents and a pilot 7 condenser so as to increase the bias of the grid circuit oi said tube, means for fully discharging 1 said condenser, means for operating said charging means in response to the operation of said relay, and means for operating said discharging means in response to the release of said relay.

5. A gain control system including a vacuum tube having a grid circuit and a plate circuit, a condenser included in said grid circuit upon which a voltage may be applied to control the bias of .said grid circuit, a tuned circuit coupled to the plate circuit of said tube for obtaining a selected current transmitted through said vacuum tube,

means comprising a relay responsive to the level of said selected current to charge said condenser in order to change'the gain of said vacuum tube in one direction, means responsive to the level of the seicctc-d current to fully discharge said condenser in order to change the gain of said vacuum tube in the opposite direction, and a rectifier connecting the plate circuit of said vacuum tube to the Winding of said relay so that the current traversing said relay winding will be the current of said plate circuit as modified by said rectifier.

J OHN' THORPE. 

